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Sep 2009

Volume 77, Issue 9, pp. 773-864

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EVOLUTION AND EARTH'S ENTROPY

Robert D. Klauber

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 773

Online Publication Date: Aug 2009

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Abstract Unavailable
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05.00.00 Statistical physics, thermodynamics, and nonlinear dynamical systems
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Resource Letter MPRT-1: Medical Physics in Radiation Therapy

Steven T. Ratliff

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 774

Online Publication Date: Aug 2009

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This resource letter provides a guide to the literature on medical physics in the field of radiation therapy. Journal articles, books, and websites are cited for the following topics: radiological physics, particle accelerators, radiation dose measurements, protocols for radiation dose measurements, radiation shielding and radiation protection, neutron, proton, and heavy-ion therapies, imaging for radiation therapy, brachytherapy, quality assurance, treatment planning, dose calculations, and intensity-modulated and image-guided therapy.
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01.30.Rr Surveys and tutorial papers; resource letters
87.00.00 Biological and medical physics

Anti-Newtonian dynamics

J. C. Sprott

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 783 | Cited 1 time

Online Publication Date: Aug 2009

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This paper describes a world in which Newton’s first and second laws hold, but Newton’s third law takes the form that the forces between any two objects are equal in magnitude and direction. The dynamics for such a system exhibit curious and unfamiliar features including chaos for two bodies in two spatial dimensions.
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05.45.-a Nonlinear dynamics and chaos
47.00.00 Fluid dynamics

Application of high-speed imaging to determine the dynamics of billiards

S. Mathavan, M. R. Jackson, and R. M. Parkin

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 788 | Cited 3 times

Online Publication Date: Aug 2009

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In spite of interest in the dynamics of the billiards family of games (for example, pool and snooker), experiments using present-day inexpensive and easily accessible cameras have not been reported. We use a single high-speed camera and image processing techniques to track the trajectory of snooker balls to 1 mm accuracy. Successive ball positions are used to measure the dynamical parameters involved in snooker. Values for the rolling and the sliding coefficients of friction were found. The cushion-ball impact was studied for impacts perpendicular to the cushion. The separation angles and separation velocities after an oblique collision were measured and compared with predicted values. Our measurement technique is a simple, reliable, fast, and nonintrusive method, which can be used to test the numerous theories for the dynamics of billiards. The addition of a spin tracking element would further broaden its capabilities.
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01.50.Pa Laboratory experiments and apparatus
47.00.00 Fluid dynamics

The rainbow as a student project involving numerical calculations

David Skålid Amundsen, Camilla Nestande Kirkemo, Andreas Nakkerud, Jørgen Trømborg, and Arnt Inge Vistnes

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 795 | Cited 1 time

Online Publication Date: Aug 2009

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It is a challenge to find interesting and realistic projects where numerical methods can be used to enhance student understanding of physical phenomena. We present such a project in which a group of students used numerical methods to analyze the physics of the rainbow. The project is suitable for students in an undergraduate physics course on the basic principles of geometrical optics. The central part of this paper is written by a group of students, and the introduction and discussion are written by their teacher. In this way both the students’ and teacher’s perspectives on using numerical methods are presented.
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42.00.00 Optics

Einstein on mass and energy

Eugene Hecht

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 799 | Cited 5 times

Online Publication Date: Aug 2009

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This paper explores the evolution of Einstein’s understanding of mass and energy. Early on, Einstein embraced the idea of a speed-dependent mass but changed his mind in 1906 and thereafter carefully avoided that notion entirely. He shunned, and explicitly rejected, what later came to be known as “relativistic mass.” Nonetheless many textbooks and articles credit him with the relation E=mc2, where E is the total energy, m is the relativistic mass, and c is the vacuum speed of light. Einstein never derived this relation, at least not with that understanding of the meaning of its terms. He consistently related the “rest energy” of a system to its invariant inertial mass.
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01.65.+g History of science
03.30.+p Special relativity

Quadrupolar contact fields: Theory and applications

C. G. Gray, G. Karl, and V. A. Novikov

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 807 | Cited 2 times

Online Publication Date: Aug 2009

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Contact terms for the electric dipole and magnetic dipole fields are well known. We give a simple derivation of the contact term of the electric quadrupole field. We then consider applications to the surface potential across a vapor/liquid interface of a nonpolar fluid, an extension of Jackson’s theorems for the mean electric fields for spherical regions of space with and without a fixed system of charges, and hyperfine interactions due to the electric quadrupole-monopole and quadrupole-quadrupole interactions of two bound particles of spin one or greater.
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41.00.00 Electromagnetism; electron and ion optics

Magnetic dipoles and electric currents

Guido Corbò and Massimo Testa

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 818 | Cited 2 times

Online Publication Date: Aug 2009

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We discuss several similarities and differences between the concepts of electric and magnetic dipoles. We then consider the relationship between the magnetic dipole and a current loop and show that in the limit of a pointlike circuit, their magnetic fields coincide. The presentation is accessible to undergraduate students with knowledge on the basic ideas of classical electromagnetism.
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41.00.00 Electromagnetism; electron and ion optics

Higher harmonic detection employing wavelength modulation spectroscopy and near infrared diode lasers: An undergraduate experiment

Gottipaty Rao, Chakrapani Gudipaty, and Daniel Martin

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 821 | Cited 3 times

Online Publication Date: Aug 2009

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Frequency modulation and harmonic detection are extensively employed in a variety of experimental techniques and offer a detection sensitivity limited only by quantum noise. We discuss a simple experiment using wavelength modulation spectroscopy and near infrared diode lasers operating in the 780 nm region to detect rubidium hyperfine spectra. Modulation spectroscopy techniques are employed to improve the signal to noise ratio for the detection of weak signals and thus significantly improve the sensitivity and specificity for detection. By using quantum cascade lasers and wavelength modulation spectroscopy, one can detect trace species at sub-ppm level, which has numerous applications in diverse areas such as medical diagnostics, food processing, industrial applications, and environmental monitoring.
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01.50.Pa Laboratory experiments and apparatus
42.00.00 Optics

Hidden momentum, field momentum, and electromagnetic impulse

David Babson, Stephen P. Reynolds, Robin Bjorkquist, and David J. Griffiths

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 826 | Cited 4 times

Online Publication Date: Aug 2009

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Electromagnetic fields carry energy, momentum, and angular momentum. The momentum density, ϵ0(E×B), accounts (among other things) for the pressure of light. But even static fields can carry momentum, and this would appear to contradict a general theorem that the total momentum of a closed system is zero if its center of energy is at rest. In such cases, there must be some other (nonelectromagnetic) momenta that cancel the field momentum. What is the nature of this “hidden momentum” and what happens to it when the electromagnetic fields are turned off?
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41.00.00 Electromagnetism; electron and ion optics

Mechanics of two pendulums coupled by a stressed spring

M. Maianti, S. Pagliara, G. Galimberti, and F. Parmigiani

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 834 | Cited 1 time

Online Publication Date: Aug 2009

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The mechanics of two pendulums coupled by a stressed spring is discussed, and the behavior for small oscillations is described. When the system is in its highest symmetry configuration, the pendulums are independent and the normal frequencies are degenerate.
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47.00.00 Fluid dynamics

Explicit gauge covariant Euler–Lagrange equation

Clinton L. Lewis

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 839

Online Publication Date: Aug 2009

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The application of a gauge covariant derivative to the Euler–Lagrange equation yields a shortcut to the equations of motion for a field subject to an external force. The gauge covariant derivative includes an external force as an intrinsic part of the derivative and hence simplifies Lagrangians containing tensor and gauge covariant fields. The gauge covariant derivative used in the covariant Euler–Lagrange equation is presented as an extension of the coordinate covariant derivative used in tensor analysis. Several examples provide useful demonstrations of the covariant derivative relevant to studies in general relativity and gauge theory.
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04.00.00 General relativity and gravitation
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An introduction to inertial navigation

William H. Baird

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 844 | Cited 1 time

Online Publication Date: Aug 2009

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In most introductory physics courses, the first equations encountered are the kinematic equations. Though the emphasis at this level tends to be on cases of constant acceleration, many real-world examples of motion are not so simple. We describe the use of inexpensive hobbyist-grade accelerometers and spreadsheet software to explore inertial navigation via numerical integration of the measured acceleration.
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01.50.Pa Laboratory experiments and apparatus
06.00.00 Metrology, measurements, and laboratory procedures

A classroom demonstration of levitation and suspension of a superconductor over a magnetic track

C. P. Strehlow and M. C. Sullivan

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 847

Online Publication Date: Aug 2009

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The suspension and levitation of superconductors by permanent magnets is a fascinating consequence of superconductivity, and a wonderful way to generate interest in low-temperature physics and electrodynamics. We present a classroom demonstration of the levitation/suspension of a superconductor over a magnetic track that maximizes the levitation/suspension time and the separation distance between the magnetic track and superconductor. The demonstration, as described, is both inexpensive and easy to construct.
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01.50.My Demonstration experiments and apparatus
74.00.00 Superconductivity

Demonstrations of analog-to-digital conversion techniques

Yaakov Kraftmakher

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 851

Online Publication Date: Aug 2009

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Two analog-to-digital conversion techniques are demonstrated using the ScienceWorkshop data-acquisition system and the DataStudio software from PASCO scientific.
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01.50.My Demonstration experiments and apparatus
84.00.00 Electronics; radiowave and microwave technology; direct energy conversion and storage

Echoes from the Moon

Luca Girlanda

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 854 | Cited 2 times

Online Publication Date: Aug 2009

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We report on a determination of the Earth-Moon distance, performed by students of an Italian high school, based on measurements of the time delay of the “echo” in the radio communications between NASA mission control in Houston and the Apollo astronauts on the lunar surface. By using open-source audio-editing software, the distance can be determined with a∼0.1% accuracy, allowing us to observe the effect of the eccentricity of the orbit of the Moon.
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01.50.Pa Laboratory experiments and apparatus
95.00.00 Fundamental astronomy and astrophysics; instrumentation, techniques, and astronomical observations

Chaos control: The problem of a bouncing ball revisited

M. Cristina Vargas, D. A. Huerta, and Victor Sosa

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 857

Online Publication Date: Aug 2009

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The problem of a body bouncing on a periodically oscillating surface is revisited to demonstrate chaos control. When the bouncing body is magnetic, it is possible to modify its behavior by adding a magnetic driving force. The mechanism of chaos control may be understood by means of a mechanical analysis which shows that the main result of applying the driving force is to shift the bifurcation diagram in such a way that chaotic behavior is replaced by periodic behavior and vice versa. A simple experiment is presented, along with a numerical simulation, that provides insight into chaos control.
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01.50.Pa Laboratory experiments and apparatus
05.45.-a Nonlinear dynamics and chaos
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Mere Thermodynamics

Don S. Lemons and Andrew Rex, Reviewer, Reviewer

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 862 | Cited 1 time

Online Publication Date: Aug 2009

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Abstract Unavailable
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01.30.Vv Book reviews
05.70.-a Thermodynamics

The Uncertainty in Physical Measurements

Paolo Fornasini and David M. Harrison, Reviewer, Reviewer

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 862

Online Publication Date: Aug 2009

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Abstract Unavailable
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01.30.Vv Book reviews
07.05.Kf Data analysis: algorithms and implementation; data management

BOOKS RECEIVED

American Journal of Physics -- September 2009 -- Volume 77, Issue 9, pp. 863

Online Publication Date: Aug 2009

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Abstract Unavailable
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